How to animate Action Clip time in 2.75?
I think what you are looking for is the animated setting for these properties. In the NLA Editor you will find an Evaluation panel in the properties sidebar N where you can enable animated for the time and influence of the strip and add keyframes.

On my first quick look at this it does appear incomplete. When you enable these two animated settings, it appears to be keyframed but there is no f-curve, but it does then allow you to add keyframes to the values which does create an f-curve that you can then adjust in the graph editor.